Process of preparing a silica organosol and resulting product



O 6 1954 R. K. .LER 2,692,863

PROCESS OF PREPARING A SILICA ORGANOSOL AND RESULTING PRODUCT Filed Nov. 23, 1951 INVENTOR.

RALPH K. ILER ATTORNEYS Patented Oct. 26, 1954 PROCESSVYOEPRZEPARIN G ASILICA YORGANOj SOL AND RESULTING PRODUCT RalphvK-h Hen, Wilmington, Del'.,':assignor tall. I. du .Pont de Nemours' and .Go'mpanm Wilminge; ton, DeL, a corporation of: Delaware ApplicationNoveniber'23, 1951, Serial No. 257,834"

2 :ClaimS-..- (Cl. 252-309) \invention relates. EtO: organoso'ls contain ing as .aadispersiomin a brine-immiscible organic liquid;colloidahparticles of amorphous silicashav: ingzan'average:diameterrzof 1 M150 millimicronsa the :apartioles being made organ'ophilic iby longt-v r hydrocarbomchaimsubstitutedi ammonium -:.base upon'thezsurfaces :of the particles; The invention is further directed to processes fonpreparingrsuch organosolsl- Organosols of sili'camade aceordingetathe-ine ventiorr arezcomposedro'f silica particleswhichiarez highly'gorganophilicr Thexsols tlm'ussprepuednm morescompati'blerin,onganicrsystems thandzhoserinr whichrvthe-particles aneless. organophilica In thed1%awing; Eigure Lillustrates 1the: -ulti,-:- 1 mate silica particles imansaquasolyand .E'igure: 2Zshows therrconditiom of silica; pane ticles-afiter they :havezbee ctreatedraccordingxto;- thetfirstvstep of. ithespresent; invention and :while theypare stilli essentially aginnamaqueous;medium; 2

invention are-substantially spherical, densegadise -.30

crete, and relatively uniforms The=-surface.ofwv theseiparticles -l 2,: 3,- 1 and 51s hydroph lic; presumably because ;ofthe surfaces-being; covered.- with- .hydroxyl (groups. n

In Figurelzl (the:- particlesvare (represented asi i spaced-apart rand in :azdispersed; and. non-.agg1;egated condition,

According to processes of the 'presentinvention a; long-hydrocarbon-chainrsubstituted ammo.-

nium base, such-ascetyl trimethylrammonium-:

bromide, is.-.addeci .to theeaquasol illustrated lin- Fi-gurel. As; shown in Figure 1-2, the-particles? I, 2, 3, 4, and 5 receiveta coating ofythe basevrep resented-tat 6' by short lines These lines. represent the s-longechain :molecule Y of the bases 4o Simultaneously with .the addition-m the-,base,-- or thereafter; 7 aamine-immiscibleorganioliquid-ais.

. added-itoathe aquasoL: As shown; inFigure 23,: then organophilic particlessare-dispersedzinathesori-fl ganic liquid. The water phase is not illustrated in the figure.

The preferred 4 aqueous sols for use according to the invention are those having particle sizes ranging from aboutslfl to.,150 millimicrons in A silicasol prepared-bylion exchange 'as in the Birds U S. l Patentv 2,244,325 is; composed of silica particles well f below 10 'millimicrons diameter:

Suchia 'sol' is not well suitedftouse in processes of i .the present invention without further" treatment.-

Since, sols of dense-particles; Which it'ds preferred to use;:may be made by'heatinga silica sol prepared.-byioneexchange -as descrilwd by Bird 1 U.:S. Patent- -2;244,-325:tosa temperature above 1 0. land: adding: furthercquantities of the same typeof 'sol" untilvtatv least fivetimes as much. silica has been; added :to :themriginal quantity as wasat first present; The panticles in: sols thus :produced arain-r excess OfI IO millimicrons' in average :diam- :etenandgdepending upon th'eiconditionsof =treatment; range upwardly to,1sa.y; about 1504milli'microns: The? particles-in: a; particular sol are sur- 1 prisingly uniform in size. The process is fully setout inithe applicatiom of 'B'echtoldand Omar: Es. Snyder- :in United-':' States application a Serial. No.l'65,536,' filed; December--15; 1948, now:

Patent No."2;5!li,902; V

Theparticles 'ofsuch'a sola'are quite denseyand:

this.rm'ay' rbe..sl'iown dnyingwtheparticles and: 'thenideterminingrth'e amount-ofinitro'gen adsorptiom Fromitheinitrogem adsorptionrit'may be de' terminedothat: the :particles have: a, .sur'facefiareasnot greatly'rinaexcess of'fthat icom-puted them *the: particle size assdetermin ed'. :by' electron micrographss it :will: be :ievidentiithat the -particlesl.

are not d'ensa but rather are; porous; then the apparent surface as determined. by nitrogen ad" sorption will. be much; higher than that. expected:

fronuthe-particle:diameterss Nitrogerradsorption,

accordingly, afiordsmnreasy :measure of the 'den sity ofithe particles: v Summarizing:.then,:=the pre ferred sole for usesas starting .materials ac'cording to-the:present.inyentiomhaveeparticles of such density that tthe surfaces-area :as determined :by

nitrogen: :a'dsorption" not rigreatlycin excess of that computedrrfor-theaparticlensize :as deter minedzby 'examination'ofanrel'ectron micrograph;

The adsorptionis'houl'd notrb'eanoree thanabout per :centagreater fthansthat :computed: from the apparent particle sizes;

The :method of. .determmingthe surface area-by nitrogenadsorptiomis: described-\ln-KA New Meth oda for Measuringrthe Surface Areas of: Finely Divided. MaterialssandsforDetermining the Size of Panticlesi; by Pi. Emmett :in Symposium on N ew :Methodsvfor Particle SizeDetennination in the *Siibsieve Range in the "-Washington== Spring' Meeting of A: SI-TB'Mz, March 4', 19451.-

Sols prepared 1 as above described ordinarily diameter and being composed of'dense particles. havea-silica-: a-l-kali ratio of fr'onr' 60 :'-1 to""t-1.

This refers to the weight ratio of total silica expressed as S102 to total alkali expressed as NazO Such sols may be adjusted with regard to pH by suitable additions of acid or removal of alkali.

Instead of the sols as above described which have extremely dense particles and very uniform particle size, one may use instead the non-uniform, non-dense type of product which can be made by precipitation of a silica gel and redispersion with alkali. Such a process is described, for instance, in the White U. S. Patent 2,375,738. The products prepared by redispersion of silica ordinarily have a good deal higher nitrogen adsorption than would be indicated by apparent diameter. This shows considerable porosity. The nitrogen adsorption is about 50 per cent greater than that computed.

Still other silica sols may be used and it will be seen that it is important only that they have a particle size from about to 150 millimicrons and that they be reasonably dense when dried. It is this latter property which sharply distinguishes them from silica gels. It is to be observed that all of the silica sols and silica particles suggested as suitable are amorphous.

A silica sol may advantageously be used which is essentially free from salts. This may be prepared, for instance by dialysis. Silica sols essentially free from salts can also be prepared by removal of cations and anions by the use of suitable ion-exchangers. Sols of this type may be made in quite concentrated form and because of their high purity are especially suitable for some purposes of the present invention. The preparation of such sols is described and claimed in United States application Serial No. 183,902, filed September 8, 1950, by Joseph M. Rule, now Patent No. 2,577,485.

The concentration of the sol may vary widely, though it will generally be desirable to use as concentrated a sol as can be handled without getting permanent precipitation or gelling or excessive precipitation during processes of the invention. Ordinarily, the sols will contain between 2 and by weight of S102. While a precipitate may be temporarily formed in the sol when the organophilizing agent is mixed with the sol, no permanent harm will be done so long as the further process steps effect a redispersion of the particles. However, where such precipitates are formed, it is desirable to conduct the steps in the process rapidly to avoid aging of the colloidal silica in a precipitated or gelled state.

In such instances, also, operation at low temperatures will be advantageous.

In order to make organophilic the particles in a sol such as those above described, there is added to the sol a long-hydrocarbonchain-sub stituted ammonium base. The base should be one which forms a water-soluble hydrochloride, that is, the hydrochloride must dissolve to the extent of, say, f per cent or more in hot water. It will also be observed that such bases will form a precipitate with silica sols when added to a concentrated silica sol at a pH of about '7.

Basic nitrogen compounds which are effective according to this invention are characterized by forming a precipitate when an aqueous silica sol having a particle size of about 17 millimicrons is tested with the solution of a salt of the nitrogen base as follows: The silica sol is diluted to a concentration of 2% SiOz by the addition of water and is titrated with a 0.5% solution of the chloride or hydrochloride salt of the nitrogen base while simultaneously adding sufiicient sodium -'primary, secondary, at least one of the r *to 20 consecutive carbon atoms.

observed that the nitrogen may be the hetero hydroxide to maintain the pH at about 8. A precipitate should result at or before the point at which there is present in the mixture the equivalent of 2 nitrogen atoms for each square millimicron of silica surface as calculated from the particle diameter and assuming a density of 2.2 for amorphous silica.

When reference is made herein to a long-hydrocarbon-chain-substituted ammonium base, it will be understood that these compounds include and tertiary amines in which hydrocarbon groups attached to the nitrogen has at least one carbon atom which is removed from the nitrogen by from 8 It is also to be atom of a heterocyclic ring.

As examples of such amines there may be named: primary amines, such as octyl, decyl, tetradecyl, and octadecyl; secondary amines, such as octylmethyl, octylbutyl, dodecylmethyl, dioctadecyl, octyl benzyl, dodecyl phenyl, and benzyl octadecyl; and tertiary amines such as octyl diethyl, dodecyl dimethyl, octadecyl dimethyl, dioctadecylethyl, dodecyl methyl benzyl, dodecyl methyl cetyl, and octyl-substituted pyridine where the octyl group is attached to a carbon atom of the ring.

Especially preferred are the long-hydrocarbon-chain quaternary ammonium bases. Again, as observed above, it is desired that these be sufficiently soluble that, for example, they will form a soluble hydrochloride as above discussed. Again, as observed above, it is desired that a quaternary ammonium base have at least 1 hydrocarbon group which has at least 1 carbon atom which is removed from the nitrogen by from 8 through 20 consecutive carbon atoms.

A preferred class of quaternary ammonium bases for use according to the invention is shown in the following formula:

Wherein,

R1 is a hydrocarbon group, saturated or unsaturated, in which at least 1 carbon atom is removed from the nitrogen by 8 through 20 consecutive carbon atoms;

R2, R3, and R4 are hydrocarbon groups containing less than 20 carbon atoms each;

R1, R2, R3, and R4 have a total number of carbon atoms which is no greater than 40; and

X is a cation, such as chloride or hydroxyl.

It is to be noted that in accordance with customary practice the various ammonium bases above described are called bases whether they are added in form of the hydroxide or in the form of one of the salts such as the chloride or hydrochloride. In any event, these are all capable of forming a true ammonium base.

Typical of the quaternary ammonium bases are: dodecyl pyridium chloride, benzyl dimethyl octadecyl ammonium chloride, cetyl dimethyl orthochloro benzyl ammonium bromide, dodecyl N-ethyl morpholinium chloride, and compounds represented by the formulae:

agooageoes The amount tofjthe ammonium base. to use. can most; easily, be determined; in..a particular. in-: stance by tit'rating. thebaseinto the. soLand lo.b'= seryihgmompletion. of. .the.tr.ansferof silica .to. an organic. phase. It will be...no.ted..ofjthisquantity, that, it;willl he the. minimum. amount. whichzisz' eifective.;.and. will. not represent a. complete 003/:- era-gebfltheparticles .in.-all. cases.v In .many. in: stancessthengroups. will. be. attached. at .separated intervalsleaving. a. number. ofii hydroxyl. groups. upon the surfaces. In. such .sols..the..transfr.to.. polar. solvents, ,such. asketones-and alcohols and amides,,proceedssatisfactorily. Eor. transfer. to. hydrocarbonsolventsa. much more complete. coverage is desired;

A large excess of the. base: is generally to be avoided because it tends to cause emulsification of the organic liquid with the aqueousphase. Generally; it -is desirable' to addno-more oi'the base than will prorvi'cle a mono layer ora little less: upon the'si-lica surface; Formost types ofor-g gani'o bases an amount cal'culated to give about 1 nitrogen atom in lthe-form of thebase for= every 25? squarev angstroms of silica surface will' pro-'-- vid'easuitably complete coverage. The exact amount will depend somewhat upon thestructure-of thebase: I'll-general, about 0fthesurface of 'tlie 'si-lica shouldbecovered; Thus; atleast -sufiicientof the-ammoniumbase should be used to provide the equivalent of 1 basic nitrogen atom for every 500: square angstroms of silica surface. Typicalquantities of benzyl dimethyl octadec-yl ammonium chloride, for. example; to berused with a silica sol made up of milli micron particl'es will'thus'range from about 4' to= 83 grams of the nitrogen base chloride-per 100 gramsof SiOa-in the-system. On theother hand; for a -silica" sol containing particles of 130'millimi'-- crons di'ameter the weight of" base ranges from minimum of. Diagram to" about 614- grams per 100 7 grams of S102;

Organic liquids which form' the organosols= of the present invention; are preferably those which will form a second liquid phase when. added to a saturated 'solutionofsodium chloride at"' (3.. witHgoodmiXing; This" is ofcoursewliat'isi meant when reference is made. to a" liquidlasbeing'iinmiscible with brine:

Suitable organic: liquids are such organic S01? vents" as the" monoliydric alcohols", such" as' nor+ malpropanol; normal butanol, isopropanol, isobutanol; tertiary 'butyl alcohol; and methylii'sobut'yP'carbinol; The alcohols can be substituted, as, fonexam'ple; such materials as.I-I'( CF2) sCl-Iz'OI-L' Ethers and substituted ethers are suitablesol vent's: For-example; there. can be used diethyl" ether; dichloroet'l'iyl ether; propylene oxide;,and so: forth. Gther suitable so'l'vems comprise ke.-- tones Jbr-exampl; acetone; methyl isopropyl'f ketone; and'methyl' ketoneyesters, such asibutyl" acetate; amidesand substituted amidesgsuoh' as 70'; dimethyl formamide.;- and ethers; ofL phosphorus oxyacids, such'as tributyl phosphate; triisoamyl phosphate; and triethyl phosphate.

Present 'a'l'sdinthe'solvent system-maybehy drocarbons"; Other-organic" solvents which' may" 75 j for. a wide variety ofuses.

tetrachloroethylene: It isr'to be noted; ofthe. hydrocarbons; and other. such. non-polarliquids:

which do: not contain: oxygenaor nitrogen. atoms:

that it will? oftenzbe= found: very. advantageous;

to include: at least: small amounts of: one of, the: polar solvents: of; the: types: previously: discussed; The organic" liquid; can: of course be: present. in: amounts: rangingrfrom .jlISti'SUfiCiBIltUtQ." proavide. ardispersiorrmediumr for'the silicatto 1181a? tively large-quantities .where a dilute; organosol is desiredi It. isxfurthers' tor. be: noted that: mix-- tures; of? these? organic liquids. may. be used ass. describedand thatzwater need. not :be separated: entirelyifrom.the'organic. liquid; A large amountof organic liquidiimayzbesuseditosefiect theaexatraction :ofi the siIic'a;. and thereafter; if desired, the orgamto: liquidr. may: be: in; part. removed; by: distillation Again transfenmay; be efiectedmm stillrother organic liquidsz. preferred:.method=. is: to; use; at. mixture; of: a. readily. volatile; poiar: liquicka mixed witnariminorgquantity. on a.highen boiling-r organicxliquidi during: the; extractionvstepg.

thereafter; removing the morev volatile come ponent, and thus obtaining a; concentratedasol: in. the. less: volatile component.

In conducti g... processes; of. the. invention. it. isnpreterredthat thepH beneanneutrality at the: timewhen the.- silica. is;v transferred to. the, 012- garlic; liquid. This is particularly, important 1 inthe. case; of Weak; organic: bases... As; for: the; quaternary ammoniumetypeeof;organic bases; the a pH is; nmchless. critical: and; may vary; withinl the range, say, from 2 to 10 although it is'still. preferred-rte be near: neutral- In. conducting. processes. of the invention. the, brine-immiscible organic solvent. will. ordinarily be.added.-to the aquasolevenbefore additionof. theebase-is begun. Duringadditionof the base; the. twolphases will. be violently, agitated and. transfer: or"- dhesilicawill-oectmcontinuously.

Alternatively, ,the. organic. base:- may bee added. insuch'amountas to, precipitate all of the silica. in the system in a form whichcanbe filtered. off, washed,.,and. then dissolved inthe organic solvent...

When. the. silica has been transferred.- to. the; organic. phase, or. even. beforethe. transfer has, been. completed, it. is oftenadvantageous to add. salt to..the sol. Sodium. chloride... sodium.nitrate,., sodium.sulf.ate-,.or. other highly soluble, neutral. salts. can. similarly beused upto. the point. of.

: saturation. These assist theseparation. of the;

silica. fi'om..the water and; thev transfer. into the. organicliquid. They simultaneously reduce the. solubility of.wat'er. inthe organicphase, .tlius .eilfecting a cleaner separation. Furthermoreitis often notedithat. the. higher; density. of. the. sat.- uratedsaltsolution permitsmore ready separate-- tioniof 'tlietwoptiases by gravity or centrifuging.

The organosols', and by this it is meant to in.- clude sols containing some water, are suitable Organosol's containing; comparatively little water can readily be in.- troduced into a wide variety of organi c media. They may be mixed with liquidor di'y lubricants, suchas hydrocarbon oils, fluorocarbon oils, silicone oils; vegetable oils,.polyether oils, graphite, talc, molybdenum sulphide, powdered" mica to give improved viscosity; wetting power body, Water resistance, and the like in many of the ordinary USES'OffthGSB. materials; Greases result when somewhat"larger-quantitiesof the organochlorinated. hydrocarbons:

sol are incorporated in these oils. fluids can also be thickened.

The organosols can be used as a means or" introducing colloidal silica as a clarifying agent and adsorbent for purification of petroleum products. It is particularly efiective, since it readily disperses in the organic medium to be treated, and yet can readily be caused to agglomerate and settle out with the impurities at the end of the process. This organosol also promotes dispersion of other types of decolorants such as clays. Vapors may also be effectively scrubbed by bubbling them through the organosols.

Fuels, particularly diesel fuels and rocket fuels, can be improved by having silica dispersed therein by means of these organosols because it provides a catalytic surface for combustion and also keeps the combustion chamber clean.

Waxes, especially those used in coating paper, are greatly improved by addition of these silica organosols. They have more body when hot, permitting thicker coatings by a single dip, and preventing blocking during hot weather. Wax compositions containing organic solvents such as paste waxes and waxes dissolved or suspended in naphthas can advantageously be modified with organosols as herein described.

Pesticides and insecticides, particularly those in organic solvents, are greatly improved by incorporation of dispersed organophilic silica in the organosol. The silica may act as a diluent, extender, carrier, activator, dispersing agent, wetting or emulsifying agent, and thickener. The latter use is particularly applicable to the preparation of pastes and salves used on farm animals.

The organosols form a vehicle by which the colloidal silica can be dispersed into molded plastics to act as a filler to improve tensile and compression and shear strength. Even transparent or translucent plastics which have an index of refraction near that of colloidal silica will retain their transparency when filled. The colloidal silica also serves to diminish the tacki- Hydraulic ness of the surfaces of plastics after molding, or

of films after extrusion.

In rubber and other linear organic polymers, the hydrophobed silica in an organosol can be dispersed directly in the latex or in monomer or low polymer solutions before polymerization.

The surface coating on the colloidal silica prevents it from adsorbing catalysts, activators, and the like, and thus does not interfere with the final polymerization or curing. The colloidal silica can also be incorporated into the finished polymer before it is spun into fibers or extruded into sheets. Tensile, tear strength, tenacity, temperature resistance, and resistance to deformation are greatly improved in these cases.

These organosols act as dispersing agents, and often modify the polymerization when incorporated into dispersions and emulsions of monomers before polymerization.

The silica dispersed in organic polymers acts as a delusterant, anti-slipping agent, and stiffening agent, and improves the penetration, retention, and color of the dyes used.

Synthetic rubbers, such as neoprene and GRS, are, of course, included in this summary.

These organosols can be combined with organic polymer-type'protective coatings, including resins, lacquers, drying oils, etc., to improve adhesion and to strengthen and harden the protective film. They are also effective in the oleoresinous paints and in the chemically-resistant polymeric coatings such as Teflon. The colloidal silica acts as a flatting agent, a dispersing and suspending agent, a thickener, a wetting agent, an extender, and the like.

The silica having an organophilized coating can be dried directly out of the aqua organosols to form a solid dry product. Where at least 50% of the surface of the silica particles has been covered with organophilic groups, these dry products can be dispersed directly into organic solvents, or into organic resins, or can be incorporated into organic solvent dispersions of other materials. While for some uses it is desirable to maintain the products in a wet condition, nevertheless there are cases in which it is desirable to dry the products and then incorporate the dry products in the composition to which it is to be added. The dry products can be directly dispersed in the various compositions above discussed with reference to organosols.

In order that the invention may be better understood, the following specific examples are given in addition to those already generally described:

Example 1 A colloidal silica sol containing 20 g. of SiOz as particles between 10' and 15 millimicrons in diameter and having a pH of about 9 was diluted to 1000 cc. with tap water, and mixed with 100 cc. of benzene. A dodecyl pyridinium chloride solution (120 cc. containing 2.4 grams of dodecyl pyridinium chloride) was then slowly added at C. Precipitation appeared to be complete when about 60 cc. of the dodecyl pyridinium chloride had been added, corresponding to 6% dodecyl pyridinium chloride on the weight of dry SiOz. The mixture was allowed to stand, but no separate benzene layer containing silica appeared; the mixture remained as an emulsion or suspension. The suspension was filtered yielding a relatively porous, moist cake weighing 1'78 grams, and therefore, containing about 11% $102. The filter cake was white and greasy to the touch. The filter cake was immiscible, upon vigorous agitation, with water, but was completely soluble in acetone, yielding a practically clear, stable, colloidal solution. Analysis showed that it contained 6.4 parts of dodecyl pyridinium chloride (or equivalent dodecyl pyridinium groups) per grams of SiOz.

Example 2 A colloidal silica solution containing 30.5% silica by weight and a pH of 9.18 and consisting of particles about 1'7 millimicrons in diameter was added in a thin stream with vigorous agitation to 10 cc. of 37% HCl. The final pH was 1.75. To 250 grams of this acidic colloidal silica solution were added 315 grams of isopropanol and 30 grams of fine sodium chloride crystals. The resulting system emulsified immediately. Twenty-five cc. of a 40% dodecyl pyridinium chloride solution were added in increments finally causing the emulsion to break and bringing about a complete separation into two layers. The resulting dodecyl pyridinium chloride/SiOz weight ratio was approximately 13/100. An additional 80 grams of isopropanol was added during the separation. The isopropanol layer (500 grams) contained 12.4% S102 and 18.6% H2O.

A portion of this isopropanol layer (365 grams) was placed in a 1-liter, 3-neck, round-bottom flask, heated over an oil bath, and fitted with an air stirrer and a distilling column. The isopropanol-azeotrope was removed by distillation, 633

grams of dry isopropanol being added to the distilling flask intermittently to maintain the volume. The product sol:(128 g.) remaining in the distilling flask at' the 'end of the run contained I279 Si')2 and 0.-60 %-"-HO. :Upen cooling -thesol :was :viscous -=-antl opaque; butreafter -=dilution with isopropanol the viscositye and turbitlity "were low. l Iheasolution wa s compatible :with benzene.

Example *3 .40 grams-.of sodium chloridaland 12 gramseof a e'solution-containing 4.8 grams.of-nodecyl ypyridin- .iumwhloride exactly as described in .:Example 2. The system separated into two layers, the upper isopropanol layer weighing 748 grams and containing 11.4% S102 and 29.9% H2O.- The lower brine layer was discarded. A 640 g. portion of the isopropanol layer was mixed with 600 grams of benzene and 50 grams of a solution containing 24.8 grams of dodecyl pyridinium chloride. The mixture again separated into two layers.

The upper benzene-isopropyl alcohol layer weighing 1064 grams and containing 8.34% silica and 5.15% water was removed in a separatory funnel and distilled as described in Example 2, using a Berl saddle packed column (30") attached to a 3-neck, round-bottom flask con- 3 taining an air driven stirrer and heated by an oil bath. The distillation was carried out over a temperature range of 65.8 to 71.0 C. to remove the benzene-isopropanol-water azeotrope which boils at 66.51 C. A 1:1 reflux ratio was employed with additions of benzene being made periodically to maintain the volume. A total of 236 grams of benzene was added to 843 grams of the mixture in the still. The product (527 grams) remaining in the distilling flask contained 13.4% S102, 0.12% H2O, benzene, and a considerable fraction of isopropanol. The product was a clear, non-viscous, light-straw colored liquid. It did not gel after many months at room temperature.

In order to prepare an alcohol-free sol, distillation of this product was continued to remove isopropanol and benzene as a binary azeotrope which boils at 71.92". Thus, 296 grams of this product were distilled over the range of 71 to 795 C. with the periodic addition of a total of' 294 grams of benzene. The benzene sol (317 g.) remaining in the distilling flask contained 12.4% S102 and 0.02% E20. This product was only slightly more turbid than that containing some residual isopropanol. It was equally non-viscous.

Example 4 A colloidal silica solution containing 30.85% silica and having a particle diameter of about 18 millimicrons was added in a fine stream, with agitation, to 5 cc. of 37% HCl. The final pH was 1.85. To this solution were added 334 grams of a tertiary butyl alcohol-water azeotrope, 100 grams of tertiaw butyl alcohol, 30 grams of sodium chloride crystals, and a total of 41 cc. of a 40% dodecyl pyridinium chloride solution, which was suflicient to break the emulsion and to eflect a good separation into two layers. The upper ornorm cc. 8: water until the game Y layer (649 grams) contalned 15. 4% Sim, 17.8% H20, and 16 grams of dodecyl pyridinium -added "by increments until separation into two layers 'again occurred. Ehetoluene tertiary butyl alcohol layer contained 7 .8% 'SiOz and 63% H2O, and 0.1% nitrogen, or about i 33 grams of dodecyl pyridinium chloride per 100 :grams ot silica.

The =azeotropic dehydration "and --alcohol recovery :were carried :out in ea set-up similar -to "that: employed in tpreparing Lthe :benzene sol 'described infixample l 'Thus,-7281grams of the ntoluene tertiary butyl 'alc'ohol :extract was :idis- "tilled over a'=range::of I76 l:to?1'08.8 0., :while 173 grams of toluene Wereaddediduri-ng-the course o1 ithe -=distillation .:.to nnaintain :the -volume (of the liquid. The stable ttoluene sol remaining in =-the distilling flask was clear and of low viscosity, and contained 14.1% $102 and less than 0.06% H2O. It was compatible with equal volumes of carbon tetrachloride, dichloroethyl ether, petroleum ether, kerosene, turpentine, ethyl ether, ethyl alcohol, normal hexanol, heptanol-2 and tetralin.

Example 5 A colloidal silica sol containing about 30% S102 and consisting of particles of about 17 millimicrons in diameter was charged into a l2-liter, three-neck flask to which was attached a 2 x 6" glass column packed with A helices. A total of 2 kg. of a colloidal silica sol (prepared according to U. S. patent application Ser. No. 65,635) containing about 30% S102 was deionized by passing through a bed of anionic ion-exchange resin, and then through a bed of cationic ionexchange resin. Two kg. of the deionized sol was diluted with 6 kg. of normal propanol and the mixture was added to the hot normal butanol at a continuous regular rate for a period of 8 hours. The column was operated at the maximum boilup rate allowable without flooding, and a reflux ratio of approximately 2.2 was used throughout the addition and dehydration steps. The latter required about 3 hours. The end of the dehydration step was signalled by the rise in the head temperature to the boiling point of normal butanol.

The dilute organosol was treated with 4% by weight of dimethyl octadecyl benzyl ammonium chloride. A three-necked, l-liter flask (equipped with a mechanical stirrer, a dropping funnel, a thermometer, and distillation head) was halffilled with the dilute organosol. While the sol was being stirred, the pressure was reduced to approximately 35 ml. and the contents of the flask were then heated by means of a water bath held at 6570 C. Distillation was carried out at constant volume by adding organosol at the same rate that the alcohol was distilled from the pot until the desired S102 concentration was reached.

The resulting sol had a high degree of stability, e. g., more than 200 hours at C. and in definitely at room temperature. It was completely compatible with benzene.

I claim:

1. An organosol of colloidal particles of amorphous silica having an average diameter of 10 to millimicrons, the particles having adsorbed upon their surfaces a long hydrocarbon-chainsubstituted ammonium ion of which the hydro- 11 chloride is Water-soluble, said ammonium ion having the formula wherein R1, R2, R3, and R4 are hydrocarbon groups containing a total of no more than 40 carbon atoms, the R1 group has at least one carbon atom removed from the nitrogen by from 8 to 20 consecutive carbon atoms, and R2, R3, and R4 contain less than 20 carbon atoms each.

2. In a process for preparing a silica organosol from an aquasol of colloidal particles of amorphous silica having an average diameter of from 10 to 150 millimicrons, the steps comprising adding an organic liquid from the group consisting of alcohols, ethers, ketones, esters and amides and a long-hydrocarbon-chain-substituted. quaternary ammonium base, the ammonium ion of the base having the formula contain less than 20 carbon atoms each, transferring the silica coated with the quaternary ammonium base to the organic liquid, and separating the liquid from water.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,515,949 Di Mais July 18, 1950 2,515,961 Marshall July 18, 1950 2,601,352 Wolter June 24, 1952 

1. AN ORGANOSOL OF COLLOIDAL PARTICLES OF AMORPHOUS SILCA HAVING AN AVERAGE DIAMETER OF 10 TO 150 MILLIMICRONS, THE PARTICLES HAVING ADSORBED UPON THEIR SURFACES A LONG HYDROCARBON-CHAINSUBSTITUTED AMMONIUM ION OF WHICH THE HYDROCHLORIDE IS WATER-SOLUBLE, SAID AMMONIUM ION HAVING THE FORMULA 